Progress report

High sensitivity and low cost human PET system: viability

tests

POCI/SAU-OBS/61642/2004

J. J. Pedroso de Lima

PET is a valuable clinical tool, namely for

detecting cancer, evaluating heart

function and assessing neurological

conditions.

PET is the most sensitive and specific

technique to visualise, in vivo, the paths

and interactions of molecules in human

tissues and organs.

PET diagnosis is based upon metabolic PET diagnosis is based upon metabolic changes in tissues or cells.changes in tissues or cells.

By imaging 18F-FDG (18F-fluoro-deoxyglucose) uptake, functional information is obtained on where

tissues are located and how active and fast-growing they are.

Whole Body PET (WBP) scans are performed mainly to survey the body for sites of metastatic cancer cells and to make accurate tumor staging encompassing the entire body.

Whole body PET of a pacient with

metastatic disease - 18F-FDG

Whole body PET of a pacient with

metastatic disease - 18F-FDG

Whole body PET - allows images of metastatic disease spread and other oncological situations in whole body projections (anterior, posterior and lateral).

The information is qualitative.

Although being widely recognized, WBP is

time consuming (takes about 30 to 40 min with existing systems), not adapted to a

systematic screening, it is often limited by the high level of statistical noise in the

images and it is felt that a better definition in the images would be a valuable step

forward.

In the project being reported, the sensitivity characteristics of a resistive

plate chamber (RPC)–PET system with wide Axial Field of View (AFOV) for human PET technology was studied through Monte Carlo simulations, complemented by an approximate analytical model, aiming at

whole-body human PET systems with AFOV in the order of 200 cm.

It was proved that the sensitivity,

dominated by the solid angle, grows

strongly with the AFOV and with the

axial acceptance angle, while the

scatter fraction is almost

independent from the geometry.

Simulations suggest that the sensitivity of such systems for

human whole-body screening, under reasonable assumptions, may

exceed the present crystal-based PET technology by a factor up to 20.

The spatial resolution of the new device is better than the existing systems and its cost much lower.

Additionally the cost-effectiveness of these detectors and their very good

timing characteristics opens the possibility to build affordable Time of Flight (TOF)–PET systems with very

large fields of view.

These characteristics show that this project is in the right direction in what concerns the development of a new concept on WBP studies, i.e., a device based upon RPCs that is faster, allowing higher patient throughput, with better spatial resolution and much cheaper than the conventional systems.

As work for the future the integration of RPC-PET in a PET-CT system is an other important goal.